SRAM cell word line structure with reduced RC effects

ABSTRACT

A device is disclosed that includes a memory bit cell coupled to a bit line, a word line, a pair of metal islands and a pair of connection metal lines. The word line is electrically coupled to the memory bit cell and is elongated in a first direction. The pair of metal islands are disposed at opposite sides of the word line and are electrically coupled to a power supply. The pair of connection metal lines are elongated in a second direction, and are configured to electrically couple the pair of metal islands to the memory bit cell, respectively. The pair of connection metal lines are separated from the bit line in a layout view. A method of fabricating the device is also provided.

PRIORITY CLAIM AND CROSS-REFERENCE

The present application is a continuation application of the U.S.application Ser. No. 15/186,446, filed Jun. 18, 2016, which claimspriority to U.S. Provisional Application No. 62/243,896, filed Oct. 20,2015, issued as U.S. Pat. No. 10,411,019 on Sep. 10, 2019, all of whichare herein incorporated by reference.

BACKGROUND

A typical static random-access memory (SRAM) device includes an array ofmemory cells arranged in columns and rows that are accessed through theoperation of word lines and bit lines electrically coupled thereto.However, the RC effects of the word lines and bit lines limit theperformance of the static random-access memory device seriously.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is an exemplary diagram of a memory array in accordance withvarious embodiments of the present disclosure;

FIG. 2A is an exemplary circuit diagram of the memory device inaccordance with various embodiments of the present disclosure;

FIG. 2B is an exemplary layout diagram of the memory bit cellcorresponding to that in FIG. 2A, without any interconnection, inaccordance with various embodiments of the present disclosure;

FIG. 2C is an exemplary layout diagram of the memory bit cell in FIG. 2Bwith interconnections coupled to the power supply and the bit lines inaccordance with various embodiments of the present disclosure;

FIG. 2D is an exemplary layout diagram of the memory device in FIG. 2A,that includes the memory bit cell in FIG. 2C with additionalinterconnections coupled to the power supply through connection metallines and the metal islands and to the word line, in accordance withvarious embodiments of the present disclosure;

FIG. 2E is a partial layout diagram of the memory device in FIG. 2D inaccordance with various embodiments of the present disclosure;

FIG. 3A is an exemplary layout diagram of a memory device in accordancewith various embodiments of the present disclosure;

FIG. 3B is a partial layout diagram of the memory device in FIG. 3A inaccordance with various embodiments of the present disclosure;

FIG. 4A is an exemplary layout diagram of a memory device in accordancewith various embodiments of the present disclosure;

FIG. 4B is a partial layout diagram of the memory device in FIG. 4A inaccordance with various embodiments of the present disclosure;

FIG. 5A is an exemplary layout diagram of a memory device in accordancewith various embodiments of the present disclosure;

FIG. 5B is a partial layout diagram of the memory device in FIG. 5A inaccordance with various embodiments of the present disclosure;

FIG. 6A is an exemplary layout diagram of a memory device in accordancewith various embodiments of the present disclosure;

FIG. 6B is a partial layout diagram of the memory device in FIG. 6A inaccordance with various embodiments of the present disclosure; and

FIG. 7 is a flow chart of a method illustrating the fabrication processof the memory device in FIG. 6A, in accordance with some embodiments ofthe present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

The terms used in this specification generally have their ordinarymeanings in the art and in the specific context where each term is used.The use of examples in this specification, including examples of anyterms discussed herein, is illustrative only, and in no way limits thescope and meaning of the disclosure or of any exemplified term.Likewise, the present disclosure is not limited to various embodimentsgiven in this specification.

It will be understood that, although the terms “first,” “second,” etc.,may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the embodiments. As usedherein, the term “and/or” includes any and all combinations of one ormore of the associated listed items.

As used herein, the terms “comprising,” “including,” “having,”“containing,” “involving,” and the like are to be understood to beopen-ended, i.e., to mean including but not limited to.

Reference throughout the specification to “one embodiment” or “anembodiment” means that a particular feature, structure, implementation,or characteristic described in connection with the embodiment isincluded in at least one embodiment of the present disclosure. Thus,uses of the phrases “in one embodiment” or “in an embodiment” in variousplaces throughout the specification are not necessarily all referring tothe same embodiment. Furthermore, the particular features, structures,implementation, or characteristics may be combined in any suitablemanner in one or more embodiments.

FIG. 1 is an exemplary diagram of a memory array 100 in accordance withvarious embodiments of the present disclosure. In some embodiments, thememory array 100 is a static random-access memory (SRAM) array. Forillustration, the memory array 100 includes a plurality of memory bitcells 110, a plurality of bit lines including, for example, BL_0, . . .and BL_n, and BL_0 , . . . and BL_n, and a plurality of word linesincluding, for example, WL_0, . . . and WL_m.

For illustration, the memory bit cells 110 are arranged in rows andcolumns. As illustratively shown in FIG. 1, each of the memory bit cells110 is disposed at an intersection of one row and one column.

Each pair of the bit lines, such as the bit lines BL_0 and BL_0 , areelectrically coupled to one column of the memory bit cells 110. Each ofthe word lines WL_0, . . . and WL_m is electrically coupled to one rowof the memory bit cells 110.

Based on the operation of an address decoder (not illustrated), one ofthe word lines WL_0, . . . and WL_m is used to select one of the rows ofthe memory array 100. One pair of the bit lines that correspond to oneof the columns of the memory array 100 are used to perform readoperation and/or write operation on the memory bit cells 110 disposed atthe intersection of the corresponding row and the corresponding column.

FIG. 2A is an exemplary circuit diagram of the memory device 200 inaccordance with various embodiments of the present disclosure. Withrespect to the embodiments of FIG. 1, like elements in FIG. 2A aredesignated with the same reference numbers for ease of understanding.

For illustration, the memory device 200 includes a memory bit cell 110in the memory array 100 as illustrated in FIG. 1, a pair of bit lines BLand BL, and a word line WL. In some embodiments, the bit lines BL and BLcorrespond to one pair of the bit lines as illustrated in FIG. 1, andthe word line WL correspond to one of the word lines WL_0, . . . andWL_m as illustrated in FIG. 1.

For ease of understanding, only one memory bit cell 110 and thecorresponding bit lines BL and BL and the word line WL are illustratedin FIG. 2A. Various numbers of the memory bit cells 110, thecorresponding bit lines BL and BL, and the corresponding word line WL inthe memory device 200 illustrated in FIG. 2A are within the contemplatedscope of the present disclosure.

In some embodiments, the length of the memory bit cell 110 ranges fromabout 2 to about 3 times the width of the memory bit cell 110. Forillustration in FIG. 2B, the length of the memory bit cell 110corresponds to a longer side of the memory bit cell 110, and the widthof the memory bit cell 110 corresponds to a shorter side of the memorybit cell 110. In some embodiments with reference to FIG. 2D, in a plainview of the memory bit cell 110, the longer side of the memory bit cell110 is parallel to the word line WL, and the shorter side of the memorybit cell 110 is perpendicular to the word line WL.

In some embodiments, the length of the word line WL is the same as thelength of the memory bit cell 110. In some other embodiments, the totallength of the word line WL in one row of the memory bit cells 110illustrated in FIG. 1 ranges from about 4 to about 300 times the lengthof one memory bit cell 110.

The lengths and/or widths of the memory bit cell 110 and/or the wordline WL discussed above are given for illustrative purposes. Variouslengths and/or widths of the memory bit cell 110 and/or the word line WLare within the contemplated scope of the present disclosure.

In some embodiments, the memory bit cell 110 is a six-transistor (6T)cell that includes transistors T1-T6.

For illustration, the transistors T1 and T3 are N-type transistors, andthe transistors T2 and T4 are P-type transistors. The transistors T1-T4are electrically coupled to operate as two cross-coupled invertersbetween a power supply VDD and a power supply VSS. In some embodiments,the power supply VDD indicates a power voltage, and the power supply VSSindicates a ground voltage.

For illustration in FIG. 2A, a first source/drain of each of thetransistors T2 and T4 is electrically coupled to the power supply VDDthrough connection points P1 and P2 respectively. A first source/drainof each of the transistors T1 and T3 is electrically coupled to thepower supply VSS through connection points P3 and P4 respectively. Thegates of the transistors T1 and T2 are electrically coupled to a secondsource/drain of each of the transistors T3 and T4 through a connectionpoint P5 and further to a first source/drain of the transistor T6. Thegates of the transistors T3 and T4 are electrically coupled to a secondsource/drain of each of the transistors T1 and T2 through a connectionpoint P6 and further to a first source/drain of the transistor T5.

The second source/drain of the transistor T5 is electrically coupled tothe bit line BL through a connection point P7. The second source/drainof the transistor T6 is electrically coupled to the bit line BL througha connection point P8. The gate of the transistor T5 is electricallycoupled to the word line WL through a connection point P9. The gate ofthe transistor T6 is electrically coupled to the word line WL through aconnection point P10.

As illustratively shown in FIG. 2A, the word line WL is electricallycoupled to the memory bit cell 110. For illustration, the word line WLis electrically coupled to gate terminals of the transistors T5 and T6,to control the transistors T5 and T6 to turn on or turn off. Through theturn-on transistors T5 and T6, the memory bit cell 110 is coupled to thebit lines BL and BL. As a result, access to the memory bit cell 110 isenabled by the word line WL which controls the two access transistors T5and T6, which, in turn, controls whether the memory bit cell 110 iscoupled to the bit lines BL and BL.

As illustratively shown in FIG. 2A, the bit lines BL and BL areelectrically coupled to the memory bit cell 110. For illustration, thebit line BL is electrically coupled to the transistor T5. The bit lineBL is electrically coupled to the transistor T6. For furtherillustration, the bit line BL is electrically coupled to thesource/drain terminal of the transistor T5. The bit line BL iselectrically coupled to the source/drain terminal of the transistor T6.The bit lines BL and BL are used to transfer data from the transistorsT1-T4 for the read operation, and/or to transfer data to the transistorsT1-T4 for the write operation.

The number and the configuration of the transistors in the memory bitcell 110 in FIG. 2A are given for illustrative purposes. Various numbersand the configurations of the transistors in the memory bit cell 110 arewithin the contemplated scope of the present disclosure.

FIG. 2B is an exemplary layout diagram of the memory bit cell 110corresponding to that in FIG. 2A, without any interconnection, inaccordance with various embodiments of the present disclosure. Withrespect to the embodiments of FIG. 2A, like elements in FIG. 2B aredesignated with the same reference numbers for ease of understanding.

Components of the memory bit cell 110 in FIG. 2B, as will be illustratedbelow, are disposed, in some embodiments, over a semiconductorsubstrate, which, for convenience of illustration, is not shown in FIG.2B. In some embodiments, the semiconductor substrate is a siliconsubstrate or other suitable semiconductor substrate.

For illustration in FIG. 2B, each of the transistors T1-T6 of the memorybit cell 110 is illustrated within a dashed line frame. The memory bitcell 110 includes gate electrodes 200, 205, 210 and 215 arranged to formgates of the transistors T1-T6. Various conductive materials used toform the gates of the transistors T1-T6 are within the contemplatedscope of the present disclosure. For example, in various embodiments,the gates of the transistors T1-T6 are formed of metals, metal alloys,metal silicides, or the like.

In some embodiments, the memory bit cell 110 further includes finstructures 220-225. The fin structures 220-225 are arranged as activeregions of the semiconductor substrate, and are arranged to formsources/drains of the transistors T1-T6 after epitaxy. The term“source/drain” is referred to as a region that is either a source regionor a drain region, in the present disclosure.

The number and the configuration of the fin structures in each of thetransistors T1-T6 in FIG. 2B are given for illustrative purposes.Various numbers and configurations of the fin structures in each of thetransistors T1-T6 are within the contemplated scope of the presentdisclosure.

For illustration, the fin structure 220 includes fin sections 220A-220Cand the fin structure 221 includes fin sections 221A-221C. The finsections 220A and 221A correspond to the first source/drain of thetransistor T1, and the fin sections 220B and 221B correspond to thesecond source/drain of the transistor T1. Alternatively stated, the finsections 220A and 221A, the gate electrode 200 and the fin sections 220Band 221B together correspond to the transistor T1.

The fin sections 220B and 221B also correspond to the first source/drainof the transistor T5, and the fin sections 220C and 221C correspond tothe second source/drain of the transistor T5. Alternatively stated, thefin sections 220B and 221B, the gate electrode 210 and the fin sections220C and 221C together correspond to the transistor T5.

The fin structure 222 includes fin sections 222A-222B. The fin section222A corresponds to the first source/drain of the transistor T2 and thefin section 222B corresponds to the second source/drain of thetransistor T2. Alternatively stated, the fin section 222A, the gateelectrode 200 and the fin sections 222B together correspond to thetransistor T2.

The fin structure 223 includes fin sections 223A-223B. The fin section223A corresponds to the second source/drain of the transistor T4 and thefin section 223B corresponds to the first source/drain of the transistorT4. Alternatively stated, the fin section 223A, the gate electrode 205,and the fin sections 223B together correspond to the transistor T4.

The fin structure 224 includes fin sections 224A-224C, and the finstructure 225 includes fin sections 225A-225C. The fin sections 224A and225A correspond to the second source/drain of the transistor T6, and thefin sections 224B and 225B correspond to the first source/drain of thetransistor T6. Alternatively stated, the fin sections 224A and 225A, thegate electrode 215, and the fin sections 224B and 225B togethercorrespond to the transistor T6.

The fin sections 224B and 225B also correspond to the secondsource/drain of the transistor T3, and the fin sections 224C and 225Ccorrespond to the first source/drain of the transistor T3. Alternativelystated, the fin sections 224B and 225B, the gate electrode 205 and thefin sections 224C and 225C together correspond to the transistor T3.

FIG. 2C is an exemplary layout diagram of the memory bit cell 110 inFIG. 2B with interconnections coupled to the power supply VDD and thebit lines BL and BL in accordance with various embodiments of thepresent disclosure. With respect to the embodiments of FIG. 2A, likeelements in FIG. 2C are designated with the same reference numbers forease of understanding. As illustrated in FIG. 2C, for simplicity, thetransistors T1-T6 of the memory bit cell 110 are only labeled as T1-T6at the respective gate electrode, without the dashed line frame.

The interconnections includes local interconnections 230-235 andcontacts 240-245. In some embodiments, the local interconnections230-235 and contacts 240-245 are formed of metals or the like. Variousconductive materials used to form the local interconnections 230-235 andcontacts 240-245 are within the contemplated scope of the presentdisclosure.

For illustration in FIG. 2C, the local interconnection 230 electricallycouples the fin section 222A, which corresponds to the firstsource/drain of the transistor T2. The contact 240 (indicating theconnection point P1) further electrically couples the localinterconnection 230 to a metal line PL. The local interconnection 231electrically couples the fin section 223B, which corresponds to thefirst source/drain of the transistor T4. The contact 241 (indicating theconnection point P2) further electrically couples the localinterconnection 231 to the metal line PL. In some embodiments, the metalline PL is configured to receive the voltage of the power supply VDD andprovide the voltage of the power supply VDD to the transistors T2 andT4.

The local interconnection 232 electrically couples the fin sections 220Cand 221C, which corresponds to the second source/drain of the transistorT5. The contact 242 (indicating the connection point P7) furtherelectrically couples the local interconnection 232 to a metal linearranged to operate as the bit line BL. The local interconnection 233electrically couples the fin sections 224A and 225A, which correspond tothe second source/drain of the transistor T6. The contact 243(indicating the connection point P8) further electrically couples thelocal interconnection 233 to a metal line arranged to operate as the bitline BL.

The local interconnection 234 electrically couples the fin sections220B, 221B and 222B. The fin sections 220B and 221B correspond to thesecond source/drain of the transistor T1 and the first source/drain ofthe transistor T5. The fin section 222B corresponds to the secondsource/drain of the transistor T2. The contact 244 (indicating theconnection point P6) further electrically couples the localinterconnection 234 to the gate electrode 205 corresponding to the gatesof the transistors T4 and T3.

The local interconnection 235 electrically couples the fin sections224B, 225B and 223A. The fin sections 224B and 225B correspond to thefirst source/drain of the transistor T6 and the second source/drain ofthe transistor T3. The fin section 223A corresponds to the secondsource/drain of the transistor T4. The contact 245 (indicating theconnection point P5) further electrically couples the localinterconnection 235 to the gate electrode 200 corresponding to the gatesof the transistors T2 and T1.

In some embodiments, the metal line PL, the bit line BL and the bit lineBL are formed within a metal one (M1) layer.

FIG. 2D is an exemplary layout diagram of the memory device 200 in FIG.2A, that includes the memory bit cell 110 in FIG. 2C with additionalinterconnections coupled to the power supply VSS through connectionmetal lines ML1 and ML2 and metal islands MI1 and MI2 and to the wordline WL, in accordance with various embodiments of the presentdisclosure. With respect to the embodiments of FIG. 2A, like elements inFIG. 2D are designated with the same reference numbers for ease ofunderstanding.

FIG. 2E is a partial layout diagram of the memory device 200 in FIG. 2Din accordance with various embodiments of the present disclosure. Forsimplicity, in FIG. 2E, only the word line WL, the metal islands MI1 andMI2 and the connection metal lines ML1 and ML2 are illustrated.

With respect to the embodiments of FIG. 2D, like elements in FIG. 2E aredesignated with the same reference numbers for ease of understanding.For ease of understanding, the layout diagram of the memory device 200is discussed below with reference to FIG. 2D and FIG. 2E.

For illustration in FIG. 2D, the numeral labels unrelated to theadditional interconnections are not illustrated, for ease ofunderstanding. The additional interconnections include localinterconnections 236-237, metal segments 250-253, contacts 246-247, vias260-261 and vias 270-271. In some embodiments, the additionalinterconnections above are formed of metals or the like. Variousconductive materials used to form the interconnections mentioned aboveare within the contemplated scope of the present disclosure.

The contact 246 electrically couples the gate electrode 210, whichcorresponds to the gate of the transistor T5, to the metal segment 252.Moreover, the via 270 (indicating the connection point P9) electricallycouples the metal segment 252 to the word line WL. The contact 247electrically couples the gate electrode 215, which corresponds to thegate of the transistor T6, to the metal segment 253. Moreover, the via271 (indicating the connection point P10) electrically couples the metalsegment 253 to the word line WL.

In some embodiment, the metal segments 252 and 253 are formed within themetal one (M1) layer. In some embodiment, the metal segments 252 and 253are configured to receive driving signals (not illustrated) to drive theword line WL. In some embodiment, the word line WL is formed within ametal two (M2) layer different from the metal one (M1) layer. Forillustration, the word line WL extends along a direction that defines arow in FIG. 1.

The connection metal line ML1 is electrically coupled through a via 260(indicating the connection point P3) to the metal island MI1, as shownin FIG. 2E. The local interconnection 236 electrically couple the finsections 220A and 221A, which correspond to the first source/drain ofthe transistor T1, to the connection metal line ML1 through a first via(not shown), the metal segment 250 and a second via (not shown), in someembodiments. For illustration, the power supply VSS is received by theconnection metal line ML1 and further to the metal island MI1 and thefin sections 220A and 221A.

The connection metal line ML2 is electrically coupled through a via 261(indicating the connection point P4) to the metal island MI2, as shownin FIG. 2E. The local interconnection 237 electrically couple the finsections 224C and 225C, which correspond to the first source/drain ofthe transistor T3, to the connection metal line ML2 through a third via(not shown), the metal segment 251 and a fourth via (not shown), in someembodiments. For illustration, the power supply VSS is received by theconnection metal lines ML2 and further to the metal island MI2 and thefin sections 224C and 225C.

In some embodiments, the metal island MI1 corresponding to one specificmemory bit cell 110 is shared with another memory bit cell 110 in, forillustration, a left column next to the specific memory bit cell 110.Furthermore, the metal island MI2 corresponding to one specific memorybit cell 110 is shared with another memory bit cell 110 in, forillustration, a right column next to the specific memory bit cell 110.

In some embodiments, the length of each one of the metal islands MI1 andMI2 is shorter than a half of the length of the memory bit cell 110. Fora numerical example, the length of each of the metal islands MI1 and MI2ranges from about 0.2 to about 0.4 times the length of the memory bitcell 110. In some other embodiments, the length of each of the metalislands MI1 and MI2 ranges from about 0.4 to about 0.7 times the widthof the memory bit cell 110. In some embodiments, the width of the wordline WL ranges from about 1 to about 2 times the length of each of themetal islands MI1 and MI2.

In some embodiments, the metal islands MI1 and MI2 are formed in themetal two (M2) layer at opposite sides of the word line WL, asillustrated in FIG. 2E.

In some embodiments, the connection metal line ML1 and ML2 are disposedin a metal three (M3) layer different from the metal one (M1) layer andthe metal two (M2) layer. In some embodiments, in a top-down sequence,the metal three (M3) layer is formed on the metal two (M2) layer, andthe metal two (M2) layer is formed on the metal one (M1) layer.

In some embodiments, the voltage of the power supply VSS is smaller thanthe voltage of the power supply VDD. In some embodiments, the voltage ofthe power supply VSS is a ground voltage. The relation of the voltagesof the power supply VSS and the power supply VDD is given forillustrative purposes. Various relations of the voltages of the powersupply VSS and the power supply VDD are within the contemplated scope ofthe present disclosure.

In some approaches, power lines are electrically coupled to the powersupply VSS to provide the voltage of the power supply VSS to the memorybit cell. The power lines are disposed in the metal layer M2 to extendalong the direction in parallel and next to the word line WL.

The capacitance between metal lines, including, for example, the wordline WL and the power lines, of the same metal layer, are referred to asinter-wire capacitance or coupling capacitance. Such a capacitance mayraise issues in deep submicron technologies because of relativelytighter pitch and relatively higher metal aspect ratios. For example,the signals transmitted on the word line WL and the power lines areaffected by the coupling capacitance. The accuracy and the speed of theread and write operations are impacted because of the coupling effectbetween the metal lines.

Compared to the approaches discussed above, by employing the metalislands MI1 and MI2 illustrated in the present disclosure, smallfragments of metal lines are disposed next to the word line WL. Nolengthy metal line is required to extend along with the word line WL.Further, since the length of each of the metal islands MI1 and MI2 isshorter than that in related approaches, the coupling effect between themetal islands MI1 and MI2 and the word line WL is decreased. As aresult, the accuracy and the speed of the read and write operations ofthe memory device 200 are higher compared to other approaches discussedabove.

FIG. 3A is an exemplary layout diagram of a memory device 300 inaccordance with various embodiments of the present disclosure. FIG. 3Bis a partial layout diagram of the memory device 300 in FIG. 3A inaccordance with various embodiments of the present disclosure.

Similar to the memory device 200 illustrated in FIG. 2D, the memorydevice 300 includes the memory bit cell 110, the bit lines BL and BL,the word line WL, the power line PL, the metal islands MI1 and MI2 andthe connection metal lines ML1 and ML2.

Compared to FIG. 2D, the memory device 300 in FIG. 3A includes cutmetals 310, 320, 330 and 340. For simplicity, in FIG. 3B, only the wordline WL, the metal islands MI1 and MI2, the connection metal lines ML1and ML2 and the cut metals 310, 320, 330 and 340 are illustrated.

For illustration, the cut metals 310 and 320 are formed at two sides ofthe metal island MI1. Moreover, the cut metals 310 and 320 partiallycover the two sides of the metal island MI1.

The cut metals 330 and 340 are formed at two sides of the metal islandMI2. Moreover, the cut metals 330 and 340 partially cover the two sidesof the metal island MI2.

A cutting process is further performed on the two sides of each of themetal islands MI1 and MI2 covered by the cut metals 310, 320, 330 and340 respectively.

By employing the cutting process based on the formation of the cutmetals 310, 320, 330 and 340, the length of each of the metal islandsMI1 and MI2 is further decreased. The coupling effect between the metalislands MI1 and MI2 and the word line WL is further decreasedaccordingly. As a result, the accuracy and the speed of the read andwrite operations of the memory device 300 are further improved.

FIG. 4A is an exemplary layout diagram of a memory device 400 inaccordance with various embodiments of the present disclosure. FIG. 4Bis a partial layout diagram of the memory device 400 in FIG. 4A inaccordance with various embodiments of the present disclosure.

Similar to the memory device 200 illustrated in FIG. 2D, the memorydevice 400 includes the memory bit cell 110, the bit lines BL and BL,the word line WL, the power line PL, the metal islands MI1 and MI2 andthe connection metal lines ML1 and ML2.

Compared to FIG. 2D, the word line WL of the memory device 400 in FIG.4A includes a zigzag shape. For simplicity, in FIG. 4B, only the wordline WL, the metal islands MI1 and MI2 and the connection metal linesML1 and ML2 are illustrated.

For illustration in FIG. 4B, the word line WL having the zigzag shapeincludes a portion 400 having a width W and a length L, in which thewidth W is the largest width of the word line WL. In some embodiments,the length L of the portion 400 is sandwiched between the metal islandsMI1 and MI2. The portion 400 is configured to fill the space between themetal islands MI1 and MI2 as much as possible to obtain a larger linewidth. In some embodiments, the word line WL having the zigzag shape hasthe width which ranges from about 1.1 to about 1.5 times the width ofthe metal islands MI1 and MI2. In some other embodiments, the largestwidth of the word line WL ranges from about 1.5 to about 3 times thewidth of the metal islands MI1 and MI2, and the smallest width of theword line WL ranges from about 1 to about 2.5 times the width of themetal islands MI1 and MI2.

In some embodiments, the word line WL having the zigzag shape may havean even larger width. However, under such a condition, the wide wordline WL results in larger area of the memory device, which isundesirable.

When the width of the word line WL is wider, the electrons are easier toflow through the metal line. Accordingly, a wider width of the word lineWL results in a smaller resistance.

The coupling effect between the word line WL and the metal islands MI1and MI2 disposed next to the word line WL not only relates to theinter-wire coupling capacitance, but also the resistance of the wordline WL and the metal islands MI1 and MI2. As a result, the word line WLof a zigzag shape having a wider length further reduces the couplingeffect. The accuracy and the speed of the read and write operations ofthe memory device 400 are further improved.

The device of claim 4, further comprising a second word line disposed ina fourth metal layer that fully covers the first word line andelectrically coupled to the first word line.

FIG. 5A is an exemplary layout diagram of a memory device 500 inaccordance with various embodiments of the present disclosure. FIG. 5Bis a partial layout diagram of the memory device 500 in FIG. 5A inaccordance with various embodiments of the present disclosure.

Similar to the memory device 400 illustrated in FIG. 5A, the memorydevice 500 includes the memory bit cell 110, the bit lines BL and BL,the word line WL having the zigzag shape, the power line PL, the metalislands MI1 and MI2 and the connection metal lines ML1 and ML2.

Compared to FIG. 4A, the memory device 500 in FIG. 5A further includes aword line WLE. For simplicity, in FIG. 5B, only the word line WL, theword line WLE, the metal islands MI1 and MI2 and the connection metallines ML1 and ML2 are illustrated.

The word line WLE is disposed in a metal layer M4 different from themetal layers M1, M2 and M3. In some embodiments, the word line WLE fullycovers the word line WL and is electrically coupled to the word line WL.In some embodiments, the word line WLE is electrically coupled to theword line WL through a metal line ML3 in metal layer M3. As a result,the word line WLE is actually a part of the word line WL.

In some embodiments, in a top-down sequence, the word line WLE isvertically overlapped with a portion of the metal island MI1 and aportion of the metal island MI2. In some embodiments, in a top-downsequence, the word line WLE is disposed over the gate electrodes 200,205, 210 and 215 illustrated in FIG. 2C.

For illustration, the presence of the word line WLE increases the widthof the word line WL. Since the word line WLE is disposed in the metallayer M4 different from the metal layer 2, the word line WLE with thelarger width does not occupy the space that the metal islands MI1 andMI2 locate.

As described above, when the total width of the word line, including theword line WL and the word line WLE, is wider, the electrons are easierto flow through the metal line. Accordingly, the formation of the wordline WL having the zigzag shapes and the word line WLE results in asmaller resistance.

The coupling effect between the word lines WL and WLE and the metalislands MI1 and MI2 disposed next to the word line WL not only relatesto the inter-wire coupling capacitance, but also the resistance of theword lines WL and WLE and the metal islands MI1 and MI2. As a result,the formation of the word line WL and the word line WLE having a widerlength further reduces the coupling effect. The accuracy and the speedof the read and write operations of the memory device 500 are furtherimproved.

FIG. 6A is an exemplary layout diagram of a memory device 600 inaccordance with various embodiments of the present disclosure. FIG. 6Bis a partial layout diagram of the memory device 600 in FIG. 6A inaccordance with various embodiments of the present disclosure.

Similar to the memory device 200 illustrated in FIG. 2D, the memorydevice 600 includes the memory bit cell 110, the bit lines BL and BL,the word line WL, the power line PL, the metal islands MI1 and MI2 andthe connection metal lines ML1 and ML2.

Compared to FIG. 2D, the memory device 600 in FIG. 6A further includesall the features mentioned above and thus includes the cut metal 310,320, 330 and 340 formed for the cutting process illustrated in FIG. 3A,the word line WL with the zigzag shape illustrated in FIG. 4A and theword line WLE disposed at the metal layer M4 illustrated in FIG. 5A. Forsimplicity, in FIG. 6B, only the word line WL, the word line WLE, themetal islands MI1 and MI2, the connection metal lines ML1 and ML2 andthe cut metal 310, 320, 330 and 340 are illustrated.

With the disposition of the metal islands MI1 and MI2, the cuttingprocess performed on the metal islands MI1 and MI2 and the wider widthof the word line WL and the word line WLE, a smaller inter-wirecapacitance and a smaller resistance of the word line are obtained.Accordingly, the coupling effect between the word lines WL and WLE andthe metal islands MI1 and MI2 is reduced. As a result, the accuracy andthe speed of the read and write operations of the memory device 400 arefurther improved.

FIG. 7 is a flow chart of a method 700 illustrating the fabricationprocess of the memory device 600 in FIG. 6A, in accordance with someembodiments of the present disclosure.

With reference to the method 700 in FIG. 7 and the memory device 600 inFIG. 6A, in operation 705, the memory bit cell 110 is formed. In someembodiments, the memory bit cell 110 is a six-transistor (6T) cell thatincludes the transistors T1-T6.

In operation 710, the bit lines BL and BL and the power line PLelectrically coupled to the memory bit cell 110 are formed in the metallayer M1.

In some embodiments, the bit lines BL and BL extend along the columndirection. For illustration, the bit lines BL is electrically coupled tothe transistor T5 of the memory bit cell 110. The bit line BL iselectrically coupled to the transistor T6 of the memory bit cell 110.More specifically, the bit line BL is electrically coupled to thesource/drain terminal of the transistor T5. The bit line BL iselectrically coupled to the source/drain terminal of the transistor T6.

The power line PL is disposed in the metal layer M1 and is electricallycoupled to the power supply VDD. The power line PL is furtherelectrically coupled to the transistors T2 and T4 of the memory bit cell110 to provide the voltage of the power supply VDD thereto.

In operation 715, the word line WL electrically coupled to the memorybit cell 110 is formed in the metal layer M2.

In some embodiments, the word line WL extends along the row directiondifferent from the column direction. The word line WL is electricallycoupled to the transistors T5 and T6 of the memory bit cell 100. Morespecifically, the word line WL is electrically coupled to gate terminalsof the transistors T5 and T6 to control whether the cell should beconnected to the bit lines BL and BL. As a result, access to the memorybit cell 110 is enabled by the word line WL which controls the twoaccess transistors T5 and T6 which, in turn, control whether the cellshould be connected to the bit lines BL and BL.

In operation 720, the metal islands MI1 and MI2 electrically coupled tothe power supply VSS are formed at opposite sides of the word line WL inthe metal layer M2.

In operation 725, the connection metal lines ML1 and ML2 electricallycoupling the metal islands MI1 and MI2 to the memory bit cell 110 arerespectively formed in the metal layer M3.

In some embodiments, the connection metal lines ML1 and ML2 areelectrically coupled to the metal islands MI1 and MI2 through vias andare further electrically coupled to the transistors T1 and T3 throughcontacts. As a result, the metal islands MI1 and MI2 provide the voltageof the power supply VSS to the transistors T1 and T3.

In operation 730, the cut metals 310, 320, 330 and 340 are formed at twosides of the metal islands MI1 and MI2 respectively such that thecutting process is further performed on the two sides of each of themetal islands MI1 and MI2 covered by the cut metals 310, 320, 330 and340 respectively.

In operation 735, the cut metals 310, 320, 330 and 340 are removed.

In operation 740, the word line WLE in the metal layer M4 that fullycovers the word line WL and electrically coupled to the word line WL isformed.

The number and the order of the operations illustrated in FIG. 7 aregiven for illustrative purposes. Various numbers and the orders of theoperations are within the contemplated scope of the present disclosure.

In some embodiments, a device is disclosed that includes a memory bitcell, a word line, a pair of metal islands and a pair of connectionmetal lines. The memory bit cell is electrically coupled to at least onebit line. The word line is disposed over the memory bit cell and iselectrically coupled to the memory bit cell. The word line is elongatedin a first direction. The pair of metal islands are disposed over thememory bit cell at opposite sides of the word line and are electricallycoupled to a power supply. The pair of connection metal lines aredisposed over the memory bit cell and cross over the word line. The pairof connection metal lines are elongated in a second direction that isdifferent from the first direction, and are configured to electricallycouple the metal islands to the memory bit cell respectively.Furthermore, the pair of connection metal lines are separated from thebit line in a layout view.

Also disclosed is a device is disclosed that includes a memory bit cell,a first word line, a pair of metal islands, a pair of first metal linesand a second word line. The memory bit cell is electrically coupled toat least one bit line. The first word line is disposed over the memorybit cell and is electrically coupled to the memory bit cell. The pair ofmetal islands are disposed over the memory bit cell at opposite sides ofthe first word line and are electrically coupled to a power supply. Thepair of first metal lines are disposed over the memory bit cell. One ofthe pair of the first metal lines crosses over the first word line andis configured to electrically couple a corresponding metal island of thepair of metal islands to the memory bit cell. The second word line isdisposed over the memory bit cell and is electrically coupled to thefirst word line through a second metal line. Furthermore, the pair offirst metal lines are not overlapped with the bit line in a layout view.

Also disclosed is a method that includes the steps outlined below. Atleast one bit line is formed as extending in a first direction andoverlapping a memory bit cell. A first word line is formed as extendingin a second direction that is different from the first direction, and asoverlapping the memory bit cell. A pair of metal islands are formed asoverlapping the memory bit cell. The pair of metal islands are separatefrom both of the bit line and the first word line in a layout view. Apair of connection metal lines are formed as being separated from thebit line in a layout view, and as partially overlapping the first wordline and the pair of metal islands.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device, comprising: a memory bit cellelectrically coupled to at least one bit line, and comprising at leastone fin structure that is elongated in a second direction andcorresponds to at least one transistor; a word line disposed over thememory bit cell and electrically coupled to the memory bit cell, andelongated in a first direction different from the second direction; apair of metal islands disposed over the memory bit cell at oppositesides of the word line, and electrically coupled to a power supply; anda pair of connection metal lines disposed over the memory bit cell,crossing over the word line, elongated in the second direction, andconfigured to electrically couple the pair of metal islands to thememory bit cell, respectively, wherein the pair of connection metallines are separated from the at least one bit line in a layout view, andin a layout view, the at least one fin structure crosses over one of thepair of metal islands.
 2. The device of claim 1, wherein the pair ofmetal islands are separated from both of the word line and the at leastone bit line in a layout view.
 3. The device of claim 1, wherein thepair of metal islands each has a maximum width along the seconddirection, and the word line has a maximum width along the seconddirection, which is greater than the maximum width of each of the pairof metal islands.
 4. The device of claim 3, wherein the maximum width ofthe word line is 1.1 to 1.5 times wider than the maximum width of eachof the pair of the metal islands.
 5. The device of claim 1, wherein thememory bit cell is disposed in a column of a memory array, and each ofthe pair of metal islands is shared by the memory bit cell and aneighboring memory bit cell in a neighboring column of the memory array.6. The device of claim 1, further comprising a power line elongated inthe second direction and electrically coupled to the memory bit cell. 7.The device of claim 1, wherein the word line comprises a zigzag shape.8. A device, comprising: a memory bit cell electrically coupled to atleast one bit line, and comprising a plurality of fin structures thatcorrespond to transistors and comprise a first fin structure and asecond fin structure; a first word line disposed over the memory bitcell and electrically coupled to the memory bit cell; a pair of metalislands disposed over the memory bit cell at opposite sides of the firstword line, and electrically coupled to a power supply; a pair of firstmetal lines disposed over the memory bit cell, wherein one of the pairof first metal lines crosses over the first word line and is configuredto electrically couple a corresponding metal island of the pair of metalislands to the memory bit cell; and a second word line disposed over thememory bit cell and electrically coupled to the first word line througha second metal line, wherein the pair of first metal lines are notoverlapped with the at least one bit line in a layout view, and in alayout view, the first fin structure and the second fin structure areseparated from the pair of first metal lines.
 9. The device of claim 8,wherein the second word line is disposed over the first word line andfully covers the first word line in a layout view.
 10. The device ofclaim 8, wherein the second word line is overlapped with a portion of atleast one of the pair of metal islands.
 11. The device of claim 8,wherein one of the pair of first metal lines is partially overlappedwith one of the pair of metal islands.
 12. The device of claim 8,wherein the pair of metal islands each has a maximum width, and at leastone of the first word line or the second word line has a maximum width,which is greater than the maximum width of each of the pair of metalislands.
 13. The device of claim 8, wherein the first word line and thepair of metal islands are disposed in a first metal layer, the pair offirst metal lines are disposed in a second metal layer above the firstmetal layer, and the second word line is disposed in a third metal layerabove the second metal layer.
 14. The device of claim 8, wherein thefirst word line comprises a zigzag shape.
 15. A method, comprising:forming at least one fin structure extending in a first direction andcorresponding to at least one transistor that is comprised in a memorybit cell; forming at least one bit line extending in the firstdirection, and overlapping the memory bit cell; forming a first wordline extending in a second direction different from the first direction,and overlapping the memory bit cell; forming a pair of metal islandsoverlapping the memory bit cell, wherein the pair of metal islands areseparate from both of the at least one bit line and the first word linein a layout view; and forming a pair of connection metal lines separatedfrom the at least one bit line in a layout view, and partiallyoverlapping the first word line and the pair of metal islands, whereinin a layout view, the at least one fin structure crosses over one of thepair of metal islands.
 16. The method of claim 15, further comprising:forming a second word line extending in the second direction, and fullycovering the first word line.
 17. The method of claim 16, whereinforming the second word line further comprises: forming the second wordline overlapping a portion of at least one of the pair of metal islands.18. The method of claim 15, wherein forming the pair of metal islandsfurther comprises: forming the pair of metal islands locating atopposites sides of the first word line.
 19. The method of claim 15,wherein forming the at least one bit line further comprises: forming theat least one bit line locating between the pair of connection metallines and between the pair of metal islands in a layout view.
 20. Themethod of claim 15, further comprising: forming a pair of cut metal linecovering a portion of the pair of metal islands; cutting the portion ofthe pair of metal islands through the pair of cut metal line; andremoving the pair of cut metal line.